题目

Some people learn a second language easily. Other people have trouble learning a new language. How can you help yourself learn a new language, such as English? There are several ways to make learning English a little easier and more interesting. The first step is to feel positive about learning English. If you believe that you can learn, you will learn. Be patient. You do not have to understand everything all at once. It is natural to make mistakes when you learn something new. We can learn from our mistakes. In other words, do not worry about taking risks, The second step is to practice your 在数列{an}中，a1=1，an+1=2an+2n．（Ⅰ）设bn=．证明：数列{bn}是等差数列；（Ⅱ）求数列{an}的前n项和Sn．